PROJECT SUMMARY Pre-adolescence marks a period of emotional and physical changes for children, especially among girls. One way to ameliorate the negative impact of these changes is through physical activity (PA), which can improve physical, emotional, and mental health, as well as increase learning, productivity, and social skills. However, only 26.1% of US adolescents meet PA guidelines (?60 min daily moderate-to-vigorous physical activity), with fewer girls meeting the guidelines than boys. Of particular concern are Latina girls, who have much higher rates of obesity compared to non-Hispanic white girls. Low activity levels in Latinas may explain their disproportionate prevalence of obesity. In addition to obesity, physical inactivity has been associated with higher rates of cardiovascular disease and more than 10 types of cancer. Factors accounting for the low PA rates among Latina girls include sex role expectations, poor parent-child communication, few role models, lack of parental support, and lack of access to PA opportunities. Parents, particularly mothers, influence their children?s activity levels by creating and supporting PA opportunities, reducing access to sedentary activities, modeling PA, and reinforcing children?s efforts to be physically active. Characteristics of the family environment, such as communication and PA parenting practices, have been found to be associated with child PA. Interventions that target these factors may increase PA in this population during critical developmental years. The proposed randomized controlled trial examines the impact of a 12-week mother-daughter intervention, Floreciendo Juntas, promoting PA in pre-adolescent Latinas compared to a control condition. The proposed mother-daughter intervention is innovative because it examines the bi-directional influence mothers and daughters have on each other?s PA, evaluates family-level factors that impact girls? PA, and explores facilitators, barriers, and strategies for program adoption and scale up. We will use an actor-partner model (i.e., Dyadic Analyses) that accounts for interdependence to examine mother and daughter influences on daughters? PA. The proposed study builds on an acceptability and feasibility study promoting daughters? PA. The primary aim will test the preliminary impact and estimate the effect size of Floreciendo Juntas on daughters? MVPA. Secondary aims will evaluate the preliminary effects of Floreciendo Juntas on potential mechanisms of change like mothers? PA, PA parenting practices, and mother-daughter communication. We will also examine the preliminary impact of the intervention on the bidirectional influence of mother-daughter PA. As an exploratory aim, we will evaluate the feasibility, appropriateness, penetration, and potential for adoption and sustainment of the Floreciendo Juntas intervention from the perspective of participating YMCAs and Recreation Centers. The findings from the proposed study will form the basis of a randomized controlled community trial and will move the field forward in identifying targets of change in preventing chronic disease in Latino communities.